Sites of Formation of the Serum Proteins Transferrin and Hemopexin G. J. Thorbecke, … , K. Cox, U. Muller-Eberhard J Clin Invest. 1973;52(3):725-731. https://doi.org/10.1172/JCI107234. Research Article Sites of synthesis of hemopexin and transferrin were determined by culturing various tissues of rabbits and monkeys in the presence of labeled amino acids. Labeling of the serum proteins was examined by means of autoradiographs of immunoelectrophoretic patterns as well as by precipitation in the test tubes employing immunospecific antisera. Good correlation was seen between the results obtained by the two different methods. The liver was found to be the only site of many tissues studied that synthesized hemopexin. Transferrin production was observed in the liver, submaxillary gland, lactating mammary gland, testis, and ovary. Find the latest version: https://jci.me/107234/pdf Sites of Formation of the Serum Proteins Transferrin and Hemopexin G. J. THORBECKE, H. H. LiEM, S. KNIGHT, K. Cox, and U. MULLER-EBERHARD From the Department of Pathology, New York University School of Medicine, New York 10016, and the Department of Biochemistry, Scripps Clinic and Research Foundation, and Division of Pediatric Hematology, University of California at San Diego, La Jolla, California 92037 A B S T R A C T Sites of synthesis of hemopexin and in iron deficiency and the decrease in inflammatory re- transferrin were determined by culturing various tis- actions (8). sues of rabbits and monkeys in the presence of labeled Preliminary findings (9, 10) suggested that hemo- amino acids. Labeling of the serum proteins was ex- pexin is formed by the liver. Previous studies in this amined by means of autoradiographs of immunoelectro- laboratory indicate that transferrin is produced in liver phoretic patterns as well as by precipitation in the test (11-14) as well as in lymphoid tissues and isolated tubes employing immunospecific antisera. Good correla- macrophages of the mouse, rat, and neonatal rabbit (15, tion was seen between the results obtained by the two 16). However, in the guinea pig (16), adult rabbit (14), different methods. The liver was found to be the only sheep (17), monkey (12, 18), and human (12, 18), site of many tissues studied that synthesized hemopexin. the liver but not the lymphoid tissue synthesized trans- Transferrin production was observed in the liver, sub- ferrin. More recent observations point to the ecto- maxillary gland, lactating mammary gland, testis, and dermal glandular tissues (19) as yet another site of ovary. transferrin synthesis. The present work aims at establishing where hemo- pexin is produced, and at determining whether trans- INTRODUCTION ferrin is formed at sites other than the liver in the rab- The two major serum proteins in heme and iron metabo- bit and monkey. Incorporation of labeled amino acid into lism are the P-glycoproteins hemopexin and transferrin. the two serum proteins by various tissues in vitro was Growing interest in the heme-binding serum protein studied by autoradiography (AR)1 of immunoelectro- hemopexin has recently developed in response to the ob- phoretic (IE) patterns (11, 20, 21). These qualitative servation that its concentration changes from the nor- data were compared with the total amount of radioac- mal in a variety of diseases. A fall, reciprocal to plasma tivity found within the proteins precipitated by their heme levels, is encountered in hemolysis (1-3) and in specific antibodies. certain porphyrias (4 and our unpublished observations), and a rise in hemochromatosis (5), diabetes mellitus METHODS (6), and malignancies (7). Clinical investigations on Animals. The animals were young adult New Zealand the effect of various disease states on the serum level rabbits. The majority of animals were male. Submaxillary of the iron-binding serum protein, transferrin, are abun- glands were taken from fetal (22 days gestation) rabbits and dant. Greatest attention has been drawn to the elevation pooled without regard to sex. Four rabbits received intra- muscular injections of 2 X 2.0 ml and four other rabbits Dr. Knight performed this work during the tenure of an 2 X 0.5 ml of paratyphoid vaccine (Wyeth Laboratories, International Public Health Fellowship 1 F05 TWO 1571- Marietta, Pa.) 12-24 hours before death. Two rabbits were 01. Her present address is Division of Surgical Science, injected intramuscularly with 2 X 2 ml turpentine and an- Clinical Research Centre, Harrow, Middlesex, England. other rabbit was bled 60 ml from the ear vein 24 h before Dr. Muller-Eberhard is a Career Development Awardee death. Such pretreatments were previously shown to stimu- of the National Institute of Arthritis and Metabolic Dis- late serum protein production in the liver (13, 14). The eases. Received for publication 20 June 1972 and in revised form 'Abbreviations used in this paper: AR, autoradiography; 25 October 1972. BGG, bovine gamma globulin; IE, immunoelectrophoretic. The Journal of Clinical Investigation Volume 52 March 1973 725 the analysis of AR of the IE patterns prepared with monkey tissue culture fluids. Development of rabbit antisera to whole human serum was previously described (12). A sheep anti- serum to whole rabbit serum was prepared in the Otisville Laboratories of the New York City Department of Health (14, 16). Analysis of culture fluids. Qualitative analyses were per- formed by the method employing AR of IE patterns (11, 12). Appropriate carrier (added once to the antigen well before application of the concentrated culture fluid) and antisera dilutions were utilized to achieve sharp precipitation arcs on the IE patterns. After washing and drying the slides, autoradiographs were documented by using Kodak Royal Pan film (Eastman Kodak Co., Rochester, N. Y.) and an exposure time of 2 wk. Semiquantitative analyses were carried out on 5.0-jl por- tions of culture fluids after addition of 5.0 IAI of a normal rabbit serum (NRS) carrier of known albumin, transferrin, and hemopexin content. In short, most of the nonspecific binding of the radioactive material was first removed by precipitation of bovine gamma globulin (BGG) and anti- BGG added at equivalence. The supernatant was collected after incubation at 4VC overnight and centrifuged in a Pr-2 International centrifuge (International Equipment Co., Need- ham Heights, Mass.) at 2400 rpm for 30 min. To a mea- sured portion of the supernate was added an amount of anti- rabbit albumin 2-3 times in excess of equivalence to the carrier albumin. The supernate of this precipitation, col- lected under the conditions described above, was divided into two equal portions. To one of each was added either anti- FIGURX 1 Autoradiographs (AR) of IE patterns prepared rabbit transferrin or anti-rabbit hemopexin, again in an with culture fluids from monkey, fetal liver (F. Li.), re- amount exceeding equivalent carrier antigen content by two- generating liver (Reg. Li.), and normal liver (Li.), using to threefold. normal human serum (Hu. S.) as the carrier. Patterns were developed by rabbit antisera to human transferrin (Transf.) The four precipitates resulting from the analysis of one and hemopexin (HPX). Note varying degrees of labeling of culture fluid were washed three times in buffered saline (pH 7.4) and were then dissolved in 0.1 ml 1 N NaOH at 560C, both proteins in these liver cultures. mixed with 2 ml Beckman Biosolve no. 2 (Beckman Instru- ments, Inc., Fullerton, Calif.), and poured into scintillation Rhesus monkey tissue cultures were the same as those de- vials. Each tube was rinsed once with 2 ml MeOH, and scribed in a previous study (14). All monkeys except one three times with 2 ml toluene fluor. These rinses were added were female. to the scintillation vials and the radioactivity measured in a Cultures. The methods for preparing tissue cultures were Parkard scintillation counter (Packard Instrument Co., Inc., described in detail elsewhere (14). 100-200 mg of minced Downer's Grove, Ill.). tissue, or 1-3 X 107 peripheral blood leucocytes were incu- Comparison of degrees of radioactivity. Comparison of de- bated in roller tubes at 37'C for 24-48 h with 2 ml of a grees of radioactivity between different proteins is not read- medium containing 1 ,uCi of L-["4C]isoleucine and L-["4C]ly- ily possible with the methods used. The autoradiographic sine each, per ml (Schwarz Bio Research, Orangeburg, method is extremely dependent on the sharpness of the pre- N. Y.; specific activity 1000-2000 AGCi/mg). After the cul- cipitation arc, which tends to be different for each indi- ture period, media were dialyzed against 0.015 M phosphate vidual protein, and on the area of the slide over which the buffer, pH 7.2, and concentrated exactly 15-fold by lyo- protein spreads itself during electrophoresis. For instance, philization. antigen excess parts of the precipitation arc such as the Antigens and antisera. The serum proteins studied are middle of the albumin arc tend to show up less dark on the readily recognized in the complex IE patterns of whole autoradiographs (Fig. 1). The grading of density of AR serum: albumin by its characteristically high concentration images was done separately for each protein. Thus a 3 + to and fast mobility, transferrin by its capacity to bind radio- 1 + for albumin does not indicate a similar intensity as does active iron (22), and hemopexin by its peroxidase activity a 3 + to 1 + for hemopexin. when complexed with heme (23). In addition, purified hemo- Comparisons between different tissues are also hindered by pexin of rabbit and human was utilized for identification (24). the fact that the specific activity of the ["4C]amino acids in Monospecific antisera to the rabbit and human proteins the cultures is greatly influenced by the amount of cold were obtained from goats and sheep according to an immuni- amino acids added to the tissue.